Shingled Cell Module (SCM) technology is a significant leap forward in PV efficiency. By eliminating busbars and overlapping cells, it packs more power-generating silicon into every square meter.
But this technology raises a critical question: how do you capture this higher power density without sacrificing the 25-year reliability your customers demand?
The key lies in mastering the intricate manufacturing process. Unlike traditional modules, the long-term performance of a shingled module is directly tied to the precision of laser scribing, the chemical properties of the Electrically Conductive Adhesive (ECA), and the exact pressure and temperature used for bonding. If one of these variables is off, you risk introducing failure modes that standard tests might miss.
This guide breaks down the critical process factors for SCM assembly. We will share insights gained from hundreds of hours of prototyping and reliability testing on our full-scale production line, showing you how to de-risk your SCM development and ensure your innovation is built to last.
The Critical Link: Choosing and Applying Electrically Conductive Adhesives (ECAs)
The shift from solder ribbons to Electrically Conductive Adhesives is the central innovation in shingled modules, but it also introduces the most significant reliability challenges. The ECA is not just a conductor; it is a structural component that must endure decades of thermal and mechanical stress.
ECA-related failures are a primary concern for module developers, often appearing as chemical degradation or debonding after damp heat testing (85°C/85% RH). The root cause can almost always be traced back to one of three factors: ECA formulation, application consistency, or the curing process.
ECA Formulation and Its Impact on Durability
Choosing the right adhesive is your first major decision. Different formulations (e.g., epoxy-based vs. acrylate-based) have distinct viscosity, flexibility (Young’s modulus), and curing profiles. At PVTestLab, our Material Testing & Lamination Trials involve subjecting different ECAs to accelerated aging protocols to compare their long-term stability. We have found that adhesives with low moisture absorption and a Coefficient of Thermal Expansion (CTE) closely matched to silicon are critical for preventing delamination during thermal cycling.
Manufacturing Insights from PVTestLab:
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Viscosity Control is Key: An ECA with inconsistent viscosity can lead to uneven application and create voids in the bond line. These voids become stress concentration points, increasing the risk of cracking.
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Curing Profile Matters: Under-cured adhesives lack the required mechanical strength, while over-curing can make them brittle. We use our industrial laminators to test and define the optimal temperature and time profiles that ensure complete cross-linking without degrading the material.
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Emerging Trends: The move towards water-based, sustainable ECAs is promising. These formulations eliminate harmful VOCs and can achieve excellent conductivity, with some reaching a volume resistivity as low as 22 μΩ/cm. We help developers validate these new materials under real production conditions.
Precision Under Pressure: Laser Scribing and Cell Bonding
With the right ECA selected, the process moves to mechanical steps that demand absolute precision. The shingled string is formed by cutting cells into strips (typically 5 or 6 per cell) with a laser, applying the ECA, and then bonding the strips together with a slight overlap.
The Nuances of Laser Scribing
The goal of laser scribing is to create a clean, crack-free edge. A poorly optimized laser process can introduce micro-cracks that are invisible to the naked eye but become catastrophic failure points once the module is in the field. Using our high-resolution electroluminescence (EL) testers, we can inspect cell strips immediately after scribing to identify and mitigate these defects before they are laminated into a full module.
Detailed view of a shingled cell string showing the precise overlap and ECA bond line under inspection at PVTestLab.
The Art of Bonding
Applying the correct pressure and temperature during the string bonding process is crucial for creating a durable interconnect. Too little pressure results in a weak bond with high electrical resistance and potential for ECA voids, whereas too much pressure can induce mechanical stress and micro-cracks in the delicate, overlapping cell edges.
Our process engineers use our Prototyping & Module Development line to fine-tune these parameters. By creating multiple small-batch prototypes with varying settings and then subjecting them to mechanical load and thermal cycling tests, we can pinpoint the optimal process window that delivers both low resistance and high mechanical stability.
Failure Modes Uncovered: What Reliability Testing Reveals
Standard IEC 61215 tests are a good baseline, but shingled modules have unique failure mechanisms that require closer inspection. Through rigorous Quality & Reliability Testing, we have identified the most common failure modes and, more importantly, traced them back to specific process variables.
Electroluminescence (EL) image from a PVTestLab test showing micro-cracks along the shingled cell edge after thermal cycling.
- Cell Cracking at the Overlap Zone:
- Symptom: Dark lines or inactive areas appearing along the bond line in EL images after thermal cycling.
- Root Cause: Often excessive bonding pressure or a CTE mismatch between the ECA and the cell, creating stress during temperature swings.
- Mitigation: Optimizing the bonding process and selecting an ECA with appropriate flexibility.
- ECA Debonding and Degradation:
- Symptom: Increased series resistance and power loss, particularly after damp heat testing. In severe cases, delamination is visible.
- Root Cause: An incomplete cure, moisture ingress from a poor ECA formulation, or contamination on the cell surface before bonding.
- Mitigation: Strict process control over ECA storage and application, combined with a thoroughly validated curing profile.
- String-to-String Short Circuits:
- Symptom: Sudden and complete power loss from an entire string.
- Root Cause: Misalignment during the layup process, causing the edge of one shingled string to contact another.
- Mitigation: Precise automated layup processes and 100% EL inspection post-layup to detect any anomalies.
By understanding these failure modes, you can design a more robust manufacturing and quality control process. The key is to move beyond simply passing a test and toward understanding the long-term behavior of your specific combination of materials and processes.
Frequently Asked Questions about SCM Manufacturing & Reliability
How do you prevent micro-cracks during the shingling process?
Prevention starts with optimizing the laser scribing parameters—power, speed, and focus—to minimize thermal and mechanical shock to the silicon. This is followed by post-scribing EL inspection to catch any defects. Finally, the bonding pressure must be carefully controlled to avoid stressing the cell edges. We validate this entire chain on our integrated production line.
What is the typical lifetime of an ECA bond compared to a solder ribbon?
A properly formulated and applied ECA bond can be just as reliable as a traditional solder joint over a 25+ year lifetime. The challenge is that ECA reliability is highly sensitive to the manufacturing process. Solder is a more mature technology with a wider process window, whereas ECAs require tighter control over curing and material handling to achieve maximum durability. This is why process validation is so critical.
Can PVTestLab simulate our specific climate conditions for reliability testing?
Yes. Our climatic chambers can simulate a wide range of environmental conditions, from the high heat and humidity of tropical regions to the extreme temperature fluctuations of desert climates. We can customize testing cycles beyond the IEC standards to provide a more accurate assessment of module reliability in your target markets.
Your Path from Concept to Production-Ready SCM
The promise of shingled cell modules is immense, with the global market projected to reach over $12 billion by 2033. But realizing that potential requires a deep understanding of the underlying process technology. Simply assembling materials is not enough; you must build an integrated system where the cell, adhesive, and process parameters work in harmony.
Instead of investing millions in an in-house pilot line, you can leverage our applied research environment to test materials, validate your design, and optimize your manufacturing process under real industrial conditions. Our German process engineers work alongside your team to transform complex challenges into reliable, production-ready solutions.
Validate your shingled module concept with confidence. Schedule a consultation with our process specialists to discuss how we can accelerate your path from prototype to production.